Philadelphia’s dense, compact live-work downtown and relatively flat topography are excellent for bicycle commuting, especially for the 42% of working residents who live and work in Greater Center City. Despite growing popularity, however, bicycling faces some challenges. Philadelphia’s 17th century street grid, narrow streets, curbside parking and relatively short blocks with frequent stops act as de facto traffic calming, keeping vehicle speeds closer to bike-friendly velocities. But the narrow streets also leave little room to insert dedicated bike lanes without removing parking or existing vehicle travel lanes. Philadelphia’s limited enforcement of many forms of illegal parking by trucks, as well as illegal behavior by cyclists, also compound the challenges.